Certain β-dicarbonyl compounds (i.e. β-keto esters and their hydroxylated derivatives) are useful as intermediates for the preparation of fine chemicals, pharmaceuticals and plant protection products such as arthropodicidal oxadiazines. Ardiropodicidal oxadiazines are disclosed in PCT Publications WO 92/11249 and WO 93/19045. Methods of preparing these compounds have also been reported in WO 95/29171, including a preparative step involving the hydroxylation of β-keto esters. However, improved preparative methods for these compounds are desirable for more economic commercial operation. Accordingly, the present invention provides an improved process to prepare hydroxylated β-dicarbonyl compounds, including those usefull in preparing arthropodicidal oxadiazines.